Rotational atherectomy guidewire

ABSTRACT

Disclosed is a guidewire particularly suited for use in rotational atherectomy. The guidewire has increased lateral flexibility in the distal region, and a substantially constant diameter throughout. The exterior diameter at any point is substantially equal to the sum of the diameter of the central core wire, and twice the diameter of the wire of the spring coil, if any, mounted thereon. At proximal portions of the guidewire, the outer spring coil may be deleted.

This application is a continuation of application Ser. No. 07/949,908,filed Sep. 23, 1992, now U.S. Pat. No. 5,287,858.

BACKGROUND OF THE INVENTION

The present invention relates generally to guidewires for catheters andthe like, and more particularly to a guidewire for use in a rotationalatherectomy procedure.

Medical catheters generally comprise elongate tube-like members whichmay be inserted into the body, either percutaneously or via a bodyorifice, for any of a wide variety of diagnostic or therapeuticpurposes. Such medical applications frequently require use of a catheterhaving the ability to negotiate twists and turns, particularly withregard to certain cardiovascular applications.

One such application, rotational atherectomy, requires manipulation of acatheter from a position outside the patient's body through extendedportions of the patient's arterial system to position a cutting tip at astenotic site. Stenosis is an abnormal narrowing of a passage or canalin the body, commonly associated with atherosclerosis, or blocking ofthe arteries with plaque.

Rotational atherectomy utilizes a rapidly rotating cutting tool at thedistal end of the catheter for transluminal recanalization ofintravascular lesions of soft or hard thrombotic or atheromatousmaterial. The procedure is more formally known as PercutaneousTransluminal Rotation Ablation (PTRA).

One commonly used rotational atherectomy device is made by HeartTechnology, Inc. and marketed under the name "Rotablator®". TheRotablator consists generally of an advancer/catheter, a guidewire, aconsole and a power source of air or nitrogen. Thousands ofmicroscopic-sized diamond crystals coat the forward face of anelliptical-shaped polishing tip. With each revolution, these crystalsremove tiny scoops of plaque from the artery. The cutting tip comes in avariety of sizes ranging from 1.25 mm to 4.5 mm.

The particles, much smaller than a red blood cell, are said not topresent a threat of injury by lodging in the patient's cardiovascularsystem. During a plaque removal procedure, only a few thousandths of apound of the tiny plaque particles are released into the bloodstream.The body's reticuloendothelial system is believed to naturally remove asmuch as a pound of impurities from the blood supply each month.

The diamond cutting surfaces are said to easily remove even the hardestcalcified plaque. The Rotablator is said to be useful for virtually alllesion types, including long, calcified, eccentric, and distal. Thepatient is left with a smooth, patent lumen. Success in the rotationalatherectomy procedure is defined as a lesion with less than 50% residualstenosis and a 20% absolute improvement in the luminal diameter.

In general, the catheter comprises a small diameter, triple-helix woundtubular shaft with a cutting tip on its distal end. An air turbinecauses the tubular shaft and cutting tip to rotate around the guidewireand within an outer Teflon sheath at speeds of up to 200,000 rpm. TheRotablator catheter tracks over a constant 0.009-inch diameter solidguidewire. The rotational atherectomy procedure produces a smooth,polished luminal hole and is said to lessen the occurrences of elasticrecoil, flaps, and vessel dissections, commonly associated with balloondilatation.

In a typical rotational atherectomy procedure, the guidewire istransluminally inserted into the brachial or the femoral artery, andadvanced to the stenotic region. The rotatable catheter is then mountedover the guidewire and advanced to the treatment site. Coronary arteriesare tortuous, have many sub-branches, and often the obstruction iseither located where the diameter of the artery is small or, by its verypresence, the obstruction leaves only a very small opening through whicha guidewire and/or catheter can be passed. Consequently, thecardiologist often finds it difficult to maneuver the guidewire orcatheter, which are typically several feet long, from the proximal end.Often, the solid guidewire used in current rotational atherectomyprocedures does not have sufficient flexibility at its tip to negotiatethe complex system of arteries within the patient.

In contrast, guidewires currently used for percutaneous transluminalcoronary balloon angioplasty applications taper from a relatively largeproximal diameter down to as little as a 0.003-inch diameter near thedistal end, thus permitting greater flexibility at the tip. However,using such a tapered guidewire is generally unsatisfactory in arotational atherectomy procedure because there is insufficient strengthat the thinned distal end of the guidewire to support the rotating burr.In addition, the loose spring coil segment which typically covers thetapered distal portion of the core wire in the known coronaryangioplasty guidewires tends to "unwind" inside rotating atherectomycatheter.

Thus, there remains a need for a guidewire which is especially suitedfor procedures such as rotational atherectomy. In particular, theguidewire should preferably be constructed in a manner such that the tipis both more laterally pliable in bending than the current rotationalatherectomy guidewires, and yet better able to support a rotating sleeveand cutting tip than prior tapered core wire angioplasty guidewires.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a guidewire such as for use in a rotational atherectomyprocedure. The guidewire comprises an elongate flexible core wire havinga proximal segment with a first diameter and at least one distal segmenthaving a second smaller diameter.

A first coil is disposed about the distal segment, and in contact orelse in close proximity with the core wire throughout the length of thecoil. Preferably, the outer diameter of the first coil is substantiallythe same as the outer diameter of the proximal segment of the core wireto provide a guidewire having a substantially uniform exterior profilethroughout. Preferably, the outer diameter of the guidewire isapproximately 0.009 inches.

In accordance with a further aspect of the present invention, there isprovided a rotational atherectomy catheter system, comprising a sourceof rotational energy, and an elongate tubular catheter having a centrallumen extending axially therethrough and rotationally linked to thesource of rotational energy.

A guidewire is movably disposed within the central lumen. The guidewirecomprises a core wire and a spring coil wrapped about at least a portionof the length of the core wire, said coil wrapped about the core wire inthe same rotational direction as the direction of rotation of thetubular catheter during operation. Preferably, the coil is wrappedsnugly against the core wire, throughout the length of the coil.

In accordance with a further aspect of the present invention, there isprovided a rotational atherectomy method. In accordance with the method,a guidewire is inserted into a body lumen and advanced to the treatmentsite. The guidewire comprises a solid core having at least onetransition thereon between a proximal segment having a first diameterand a distal segment having a second diameter. A coil is snugly wrappedaround the distal portion of the core wire, and comprises a coil wirehaving a diameter such that the exterior diameter of the coil issubstantially the same as the exterior diameter of the proximal segmentof the core wire.

A rotational atherectomy catheter is thereafter advanced distally overthe guidewire, and the catheter is thereafter rotated in the samerotational direction as the loops of the coil, so as to preventunwinding of the coil under the rotational force of the rotationalatherectomy catheter.

These and further features and advantages of the present invention willbecome apparent from the detailed description of preferred embodimentswhich follows when considered together with the attached drawings andclaims.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view illustrating the components of a typicalrotational atherectomy system including the improved guidewire of thepresent invention.

FIG. 1a is a detail of the distal end of the catheter of the system ofFIG. 1 with the guidewire extending through the ablating burr.

FIG. 2 is a partial cutaway view of a blood vessel showing a rotationalatherectomy being performed in conjunction with the improved guidewireof the present invention.

FIG. 3 is a cross-sectional view of the distal end of the guidewire ofthe present invention taken along line 3--3 of FIG. 1.

FIG. 4 is a detail of the terminal end of the guidewire of FIG. 3.

FIG. 5 is a detail of a distal portion of the guidewire of FIG. 3illustrating the attachment of the safety ribbon.

FIG. 6 is a simplified cross-sectional view of an alternative embodimentof the guidewire.

FIG. 7 is a simplified cross-sectional view of a second alternativeembodiment of the guidewire.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a rotational atherectomy device 20including an improved guidewire 22 of the present invention. Theguidewire 22 is particularly suited for use in the device 20, however,the description of the present invention in the context of a rotationalatherectomy procedure is not meant to be limiting. Similar surgical orother procedures benefitting from a guidewire with the propertiesdescribed herein are within the range of applications of the presentguidewire 22.

The rotational atherectomy device 20 generally comprises a tubular body24, having an internal drive motor (not illustrated) within an axiallyslidable housing 26. A handle 27 is connected to the housing 26 toadvance and retract the rotating tip as will be discussed. A shaft (notillustrated) of the handle 27 extends through an upper elongated slot 30to link the handle 27 to the slidable housing 26. An elongated catheterbody 32 extends from a flexible sleeve 34 at the distal end of the body24. A pair of lower outwardly extending feet 28 with mounting holes 29provide means to attach the tubular body 24 to an operating supporttable.

A console (not shown) controls and monitors the drive motor via air hose50 which is attached to the internal slidable housing 26 through anelongated slot 33 on the side of the tubular body 24. The slot 33 on theside of the tubular body 24 is slightly longer than the upper elongatedslot 30 for the handle 27 to accommodate the full travel of the handle27 without impacting the air hose 50 or conduit 54 with the tubularbody. The proximal portion of the guidewire 22 is shown extending outthe rear face 35 of the tubular body 24, and the guidewire extends in anunobstructed path through the tubular body and the entire length of thecatheter 32.

As seen in FIGS. 1 and 2, the catheter body 32 further comprises anouter sheath 40, a rotatable hollow tubular sleeve 42 sized to rotatewithin the sheath 40. The guidewire 22 is removably disposed within acentral lumen of the rotatable sleeve 42. The rotatable sleeve 42 may bea solid-walled tube, or, preferably, a coil such as a triple-helix woundmatrix of wires defining the central lumen.

Referring to FIG. 1a, a cutting burr 44 typically comprises a rotatablesupport structure 46 coated with fine diamond crystals 48 or othercutting surface. Burr 44 is affixed at the distal end of the rotatablesleeve 42. In a typical procedure, the rotatable sleeve 42 turns thecutting burr 44 at speeds of up to 200,000 rpm. The cutting burr 44works on the principle of differential cutting--a process by which thetiny diamond crystals 48 preferentially ablate the inelastic plaquewhile the healthy elastic arterial wall deflects away unharmed.

The drive motor inside tubular body 24 is coupled to the rotatablesleeve 42 in order to impart rotation thereto. The motor may be poweredby any of a variety of known means; however, an air-driven turbine ispreferred for its high-speed, low-vibration and low-inertiacharacteristics. Thus, in a preferred embodiment, an air hose 50attaches to the slidable housing 26 within tubular body 24 such asthrough a fitting 50a. The air hose 50 provides pneumatic power to theair driven turbine. A pair of fiber optic conduits 52 also attach to theside of the slidable housing 26 through a fitting 52a to monitor thespeed of the turbine. The rotational speed information is processed anddisplayed at the console.

A sterile fluid connection 54a is also provided in the side of theslidable housing 26 to attach an IV conduit 54 through which salinesolution or other fluid may be supplied, the flow rate being controlledeither through the console or through other means known in the art. Thesaline solution is applied to the cutting site such as by flowing withinthe stationary outer sheath 40 to both lubricate the rotating burr 44and reduce the heat generation at the operating site, and also to reducefriction between the rotating catheter sleeve 42 and outer sheath 40.

A brake assembly 36 allows the surgeon to easily halt the rotation ofthe motor and rotatable sleeve 42 on demand. The brake assembly 36 iscontrolled with a shaft 37 having opposing thumb and forefinger members38 near the rear end 35 of the tubular body 24 which, by depressing oneor the other, alternately apply and release the brake. Typically, abraking mechanism would include some means for shutting off the flow ofair through the air hose 50 by pinching the flexible hose. Uponapplication of the brake 36, the rotating burr 44 and sleeve 42 stoprelatively quickly as the air-driven turbine has a very low inertia.However, the same low inertia enables the air turbine to be brought upto operating speed very rapidly when the brake 36 is released.

A suitable rotational atherectomy system for use with the guidewire 22of the present invention can be obtained from Heart Technology,Bellevue, Wash., under the trade name Rotablator®.

The rotational atherectomy procedure for ablating a plaque depositwithin an artery is generally accomplished as follows. The distal tip ofthe guidewire 22 is typically first prebent and then inserted into asmall incision in the femoral or brachial artery, and advanced to thestenotic region. The surgeon manipulates the guidewire 22 through oftentortuous, convoluted arterial passageways to the obstruction by torquingor otherwise steering the guidewire 22. A radio opaque marker or otherindicator is used to assist the surgeon in locating the distal tip ofthe guidewire 22 and positioning it at the stenotic region.

After the guidewire 22 is in position, the catheter 32 is advanced overthe proximal end of the guidewire 22 and distally into the patient, withthe wire 22 extending through the lumen of rotatable sleeve 42. Thecatheter 32 is advanced distally until the burr 44 is positioned nearthe treatment site.

As illustrated in FIG. 2, the removal of plaque 60 is accomplished byrotating the sleeve 42 to cause the burr 44 to scrape against thenarrowed walls of the deposit. The handle 27 connected to the internalslidable housing 26 allows the surgeon to longitudinally advance orretract the rotating sleeve 42 and burr 44 within the outer sheath 40and over the guidewire 22. The surgeon is thus able to nudge therotating burr 44 slowly across the plaque deposit 60 while experiencinga certain tactile feedback through the handle 27. The longitudinaldistance traveled is limited by the length of the elongated slots in thetubular body 24, which may be made shorter or longer depending on theanticipated size of deposit 60. Clinical statistics have shown thatapproximately 50% of lesions are less than 5 cm long.

The stationary outer sheath 40 extends distally to a point just proximalof the operating burr 44, and protects the vascular intima 62 frominjury while allowing the sleeve 42 to rotate with minimal frictionwithin. The ablation procedure is generally relatively short, once theguidewire is in place, such as within the range of from about 1 minuteto about 15 minutes, rendering the time spent in location and placementof the guidewire 22 a significant portion of the procedure time.

Referring to FIG. 3, the preferred guidewire 22, in accordance with thepresent invention, generally comprises an elongate core wire 70 having aspring coil 72 wound around at least a distal portion thereof. The corewire 70 is preferably a solid wire having a proximal section 70a of itslength with an outside diameter suitable for passage through theguidewire lumen of catheter 32, rotating sleeve 42, and cutting burr 44.In general, the diameter of proximal portion 70a will be no more thanabout 0.012 inches, and preferably is no more than about 0.009 inchesalthough other sizes can be readily envisioned depending upon theintended application.

A transition taper 74 separates a reduced diameter portion 76 from theproximal section 70a. The view of FIG. 3 is out of scale to facilitateillustration. In one embodiment, the length of the proximal portion 70aof the wire 22 is approximately 2.7 m, and the length of the distalportion (from the transition taper 74 to the tip 22b) is approximately30 cm.

At least one section of outer spring coil 72 is wrapped around thereduced diameter portion 76. The coil 72 may be tightly wrapped aroundthe portion 76, or pre-wound and slidingly fitted over the portion,depending on the particular manufacturing method, as will be describedbelow. Coil 72 extends distally from the transition taper 74. The coil72 is sized such that when wrapped around reduced portion 76, the outerdiameter of the coil 72 is substantially the same as the outer diameterof the proximal solid portion 70a of the core wire to produce aguidewire having a substantially uniform diameter throughout. The coil72 is preferably in contact with the reduced core wire section 76throughout the length of the coil 72, and preferably, the coil is snuglyfitted against the core. Alternatively, the coil 72 is slidingly fittedover the reduced section 76 with a slight clearance and thus is incontact due to the force of gravity.

The coil 72 is rotationally fixed with respect to the core wire 70 suchas by securing the proximal end 72a of the coil to the transition taper74 with solder or other means known in the art. Likewise, the distal end72b of the coil is preferably attached to the core wire 76 with solder,brazing or other means known in the art. Alternatively, the coil 72 canbe secured throughout its length to the core wire 76, or at specific"spot welds" periodically along its length. Preferably, however, thecoil 72 is attached to the core wire 76 only at the ends of the coil,since this advantageously optimizes the lateral flexibility of thedistal region of the guidewire 22.

The spring wrapped reduced diameter portion 76 of core wire 70, inaccordance with the present invention, results in a more laterallyflexible region at the distal end of the guidewire 22 when compared tocurrently used solid core wires of constant equivalent diameterthroughout. The improved flexibility of the distal region facilitatesthe navigation of the guidewire 22 through the arterial network, muchlike the tapered core wire guidewires for balloon angioplastyprocedures. Unlike conventional PCTA guidewires, however, the presentinvention provides sufficient support for a rotational atherectomycatheter, and does not tend to unwind while carrying an outer rotatingsleeve.

The present inventors have determined that winding the coil 72 around atleast a distal segment of central core wire 70 can provide an assembledguidewire 22 having a substantially constant diameter throughout, yetadds only minor lateral stiffness to the tapered core at this region.The coil 72 does, however, add significantly to the ability of theguidewire to support the rotating burr 44. This is due to thesubstantially continuous cross-sectional area of material the coil 72provides when it is torqued and tightens against the core wire 70. Thecoil 72 may have some clearance with the core wire 70. Thisconfiguration results in only a minimal reduction in torsional strengthat the section with the coil wire 72. Upon rotation of the rotatablesleeve 42, the flexible region resists knotting or kinking fromfrictional forces generated between the two members, and substantiallyeliminates the possibility of torsional failure.

Extending distally from the reduced portion 76 of the core wire, atleast one additional diameter reduction such as taper 78 narrowsradially inwardly in the distal direction. The first coil 72 ispreferably soldered to the core wire at about the proximal end ofelongated taper 78. The taper 78 preferably terminates in a generallyconstant diameter portion 80 at the very distal tip of the core wire.This constant diameter tip 80 is optimally flattened between rollersduring manufacturing to form a ribbon.

In the embodiment illustrated in FIG. 3, a second coil 82 extends fromabout the distal end 72b of the first coil 72 to the distal tip 22b ofthe guidewire 22. Preferably, the second coil 82 overlaps the first coilwire 72 to facilitate attachments as will be discussed. The insidediameter of coil 82 is approximately equal to the outer diameter of thefirst coil 72. The second coil 82 terminates at the distal tip 22b whereit is preferably provided with a hemispherical solid plug 84, generallyconsisting of solder. The second coil wire 82 thus encloses the distaltip 80 of the core wire 70. The second coil 82 permits an added amountof lateral flexibility at the extreme distal end of the guidewire.

As seen FIG. 3, a safety ribbon 86 preferably extends from the distalportion of the first coil 72 to the distal tip 22b of the guidewire. Thesafety ribbon 86 is affixed at both its proximal and distal ends as isknown in the art. The safety ribbon 86 thus provides a means forretracting the distal tip 22b of the guidewire in case of a break insecond coil 82.

Suitable core wire may be prepared in any of a variety of manners whichcan be readily devised by one of skill in the art. In one embodiment, aspring hardness solid stainless steel wire of 0.009 inch diameter and300 cm length is obtained from sources known to those of skill in theart. The core stock is thereafter preferably straightened such as byStarguide of Denver, Colo.

The straightened wire is thereafter ground to the desired profile suchas by Microguide, Tahachepi, Calif. Preferably, the reduced portion 76is ground to a diameter of about 0.0054 inches, so that when wrappedwith 0.0017 inch coil wire, the assembled diameter through the coil 72will be slightly less than 0.009 inches.

The transition 74 is thereafter inspected for structural integrity. Thetransition 74 typically has an axial length of about 2.5 mm andseparates the milled 0.0054 inch reduced outside diameter portion 76 ofthe core wire. The elongated taper 78 begins approximately 12 mm fromthe distal tip of the core wire. The elongated taper 78 extends about 8mm in the distal direction from the 0.0054 inch milled portion 76 to a0.0025 inch diameter tip 80. The constant diameter tip 80 of the corewire has a length of about 4 mm, and is flattened between rollers to adimension of approximately 0.001 by 0.005 inches. Of course, alternativetechniques and design specifics can be readily envisioned by those ofskill in the art, which also embody the present invention.

The coil 72 is thereafter wound or mounted around the reduced centralcore 76 such that the loops of the coil extend in the direction ofrotation of sleeve 42 to prevent an unwinding action. Winding the coil72 in this direction further strengthens the guidewire 22 torsionally asthe rotating sleeve 42 tends to tighten the coil around the central core76.

The coil 72 may be constructed in any of a variety of ways known in theart, such as by tightly winding a coil of wire directly around thecentral core 76, or by separately winding the coil and mounting the coilonto the core wire as a separate step. In the latter method, the coil 72is preferably wound around a rotating mandrel having a diameter equal toor slightly smaller than the diameter of milled segment 76, to ensure asnug fit in the assembled wire.

Preferably, 0.0017 inch diameter wire stack is wound into a coil over a0.005 inch diameter mandrel. The coil springs open slightly upon releasefrom the mandrel to approximately a 0.0054 inch inside diameter. Thecoil 72 is thereafter slid onto the core wire 70, and soldered at thetransition taper 74 and at the proximal end of the elongated taper 78.At least the solder joint 88 at the proximal end of the elongated taper78 is a high temperature solder, for reasons that will follow.

A 0.001 inch by 0.003 inch safety ribbon 86 is held in position asillustrated in FIG. 3 and in more detail in FIGS. 4 and 5. The secondcoil 82, which in this embodiment has a length of about 20 mm and anoutside diameter of about 0.014 inches, is advanced proximally over thedistal end of the core wire 70 to trap the proximal end of ribbon 86 asillustrated. The safety ribbon 86 and second coil 82 are soldered 90 tothe first coil at the proximal end of the elongated taper 78, using arelatively low temperature solder. This is so that the step of solderingthe outer coil 82 and the safety ribbon 86 into place does not reliquifythe solder joint 88 which already exists at about that point. The safetyribbon 86 extends in between the two coils, and into the solder joint.The distal opening of the second coil, with the safety ribbon 86extending therethrough, is closed by the solder plug 84 which forms thetip 22b of the guidewire. Any excess ribbon 86 is cut off at this pointand also at the first solder joint.

The reduced milled portion 76 of the core wire preferably has a diameterwithin the range of from about 0.0052 to about 0.0056 inches. Sectionshaving a diameter as low as about 0.0045 inches will probably alsoexhibit the beneficial features of the present invention, when combinedwith an appropriately sized outer coil in order to make the outsidediameter of the coil equivalent to the proximal solid portion 70a of theguidewire 22. The maximum diameter of the reduced segment 76 of the corewire is limited by the minimum diameter acceptable for the adjacent coil72. This minimum diameter is, for example, limited by the strengthrequirements of the coil 72.

Since the inside diameter of the coil 72 can be either increased ordecreased by rotating one end of the coil with respect to the other end,the precise relationship between the native ID of the coil 72 and thecore wire 70 is strongly influenced by manufacturing preferences.Preferably, the coil 72 has a sufficient native ID that it can beslidably mounted onto the core wire 70 with relative ease. One end isthen affixed to the core wire 70 and the second end may be rotated ifnecessary to bring the body of the coil in snug contact with the corewire before affixing the second end. This snug fit is preferred, howeversome minimal clearance between the coil 72 and core wire 70 ispermitted, such clearance, however, may not exceed the thickness of thecore wire.

The coil 72 preferably comprises a high tensile strength wire of aresilient, non-corrosive metal such as stainless steel, titanium orplatinum, and may have a circular cross section with a diameter of fromabout 0.001 to 0.003 inches. The wire may alternatively have arectangular cross section of from about 0.001 to 0.003 inches by fromabout 0.001 to 0.004 inches, or other variations known in the art.Preferably, the diameter of the coil stock is selected such that theassembled guidewire has a substantially uniform external diameterthroughout.

The exterior surface of the wound coil-type guidewire shaft ispreferably smooth throughout, and optionally provided with an elastic,biocompatible coating or sheath to enhance the smooth outer surface.Suitable coatings can be formed by dipping, spraying or wrapping, andheat curing operations, as are known in the art. Alternatively, heatshrinkable tubing may provide a suitable outer sheath in someapplications. A coating material should be selected which will permitsufficient flexing of the wire without cracking, will minimize slidingfriction of the implement during insertion and removal, and issubstantially chemically inert in the in vivo vascular environment. Avariety of suitable materials are known, including, for example,polytetrafluoroethylene, urethane or polyethylene.

Bench tests of a 0.009 inch diameter guidewire in accordance with thepresent invention have shown its distal end to be approximately fivetimes more flexible than the conventional solid 0.009-inch diameterrotational atherectomy wire. Tests have also shown that the torquecapacity of the distal end of the improved wire of the present inventionis approximately four times greater than the conventional guidewire intortuous passages. Thus, the guidewire shown is both more flexible inbending, yet with better torque characteristics than the conventionalsolid uniform diameter guidewire conventionally used in rotationalatherectomy procedures.

An alternative embodiment of guidewire is shown in simplified form inFIG. 6. Each of the embodiments shown in FIGS. 6 and 7 preferably arealso provided with an entry coil, such as coil 82 in FIG. 3, tofacilitate negotiation of branched passageways. The entry coil (notillustrated) preferably has dimensions on the order of 0.014 inchesdiameter by 2 cm length, although other dimensions can readily also beused, depending upon the intended application.

The embodiment of FIG. 6 generally comprises an elongate core wire 154having a spring coil 156 wound around at least a distal portion thereof.The core wire is preferably a solid wire having at least one distalsegment with a reduced diameter. In the illustrated embodiment, proximalsolid shaft portion 158 is separated from a relatively reduced diameterdistal region 151 by a tapered transition portion 160.

The coil 156 is wrapped around the central core 154 at the distalsegment 151. The coil 156 is preferably in partial contact or else inclose proximity with the core wire throughout the length of the coil,and more preferably, the coil is snugly fitted against the core alongthe length of the coil.

Referring to FIG. 6, one specific embodiment of the present inventioncomprises a guidewire 22 having a proximal segment 58 with a length ofabout 150 cm and a diameter of approximately 0.009 inch. A distal 30 cmsection of the core wire has a diameter of about 0.006 inch and a taperis provided between the two sections. The tapered transition occurs overan axial length of about 2.5 mm. Although the length of the taper doesnot appear to be critical, the risk of fracture appears to increase asthe taper approaches a right angle shoulder transition. In addition, anexcessively long taper may result in an undesirably inflexible distaltip of the guidewire, depending upon the intended application.

Coil 156, soldered at both ends to the core, comprised 0.0015-inchdiameter round stainless steel wire having a tensile strength of 444Kpsi, obtained from Fort Wayne Metals and identified as type 3040. Thewire was wound about a 0.0055-inch mandrel. The external diameter of thefinished wire was approximately 0.009 inch throughout.

Referring to FIG. 7, an alternative guidewire 168 comprises a solid corewire 170 having a proximal portion 172, at least one intermediateportion 174 and a distal portion 176. The flexibility of the guidewire168 increases from the proximal portion 172 to the intermediate portion174, and further in the distal portion 176. The principles andconstruction of the guidewire 168 are similar to the embodimentdescribed above resulting in an even more flexible tip. Thus, theproximal portion 172 transitions to a smaller diameter intermediateportion 174 which, in turn, transitions to an even smaller distalportion 176 terminating in a tip 178. Two tapered steps 180, 182 providethe reduction in diameter.

In this embodiment, two different coils made form different diameterwire stock are wound around the core wire 170 at portions 174 and 176 sothat the outer diameter of the assembled guidewire 170 remainssubstantially constant throughout. A first coil 184 is attached to thefirst taper 180 with solder and extends distally to at least one secondpoint of attachment at or near the second taper 182 or to a second coil186. The second coil 186 extends from the second taper 182 to the tip178 and is soldered thereto. A distal taper such as tapered portion 78(FIG. 3) may also be provided although for simplicity it has not beenillustrated in FIGS. 6 and 7.

The embodiment in FIG. 7 illustrates a guidewire 168 having a torsionalstrength which is relatively constant along its entire length yet havinglateral flexibility which increases in steps to the distal tip 178. Theincreased flexibility of the guidewire 168 further facilitatesnegotiation of the most complex arterial networks.

Other configurations are contemplated which more continuously increasethe flexibility of the guidewire 170. For instance, a third, fourth ormore flexible segments may be provided in the core wire. Alternatively,the central core wire may taper smoothly from the proximal segment 172to the tip 178 without steps in diameter, and a coil made from wire witha continuously increasing diameter mounted around the core to retain theouter diameter of the shaft. Alternatively, distal portion 176 can bewrapped with two layers of the same diameter wire which is used to wrapintermediate portion 174. In an embodiment having an exterior coating,minor diameter deviations such as at the transition point between coilswound from different wire stock can more easily be tolerated.

For most rotational atherectomy procedures, the guidewire, in accordancewith the present invention, is provided with a substantially uniformexterior diameter throughout. Thus, any transitions between solid outercore wire surfaces and spring coils, or between adjacent sections ofspring coil, are preferably provided with a smooth exterior surface.This can be accomplished, in an embodiment having all metal parts, byflowing solder into the transition, followed by an optional polishing orgrinding step. Although the embodiments disclosed herein have been interms of metal core wires and metal coil, non-metal materials such aspolymers, may also be utilized to construct the guidewires of thepresent invention, provided the physical properties of the materialsused are suitable under the intended use environment..

At any particular point along the length of the guidewire, the outsidediameter is substantially equal to the outside diameter of the core wireat that point, plus twice the diameter of the wire from which the coilstock was manufactured. As has been discussed, the proximal portion ofthe guidewire generally does not have an outer coil; however, an outercoil can be provided the entire length of the guidewire if desired.

In this manner, interior space such as between the core wire and anouter coil has been substantially eliminated, and the resultingessentially solid guidewire has optimal torque transmission andresistance to rotation properties. As will be apparent to one of skillin the art, this physical characteristic is desirable along any portionof the guidewire which will carry a rotating atherectomy sleeve. Thus,in an application where the guidewire projects distally beyond the endof the rotating burr 44, conventional floppy tips can be utilized inplace of the high density, low interstitial space design disclosedherein.

Although this invention is described in terms of certain preferredembodiments, other embodiments that will be apparent to those ofordinary skill in the art are also within the scope of this invention.Accordingly, the scope of the invention is intended to be defined by theclaims that follow.

We claim:
 1. A flexible atherectomy guidewire for use with a rotatingcutting element, comprising:an elongate flexible core wire with aproximal segment having a first diameter and at least one distal segmenthaving a second, smaller diameter; a first coil disposed in its entiretyabout the distal segment, the first coil having a proximal end and adistal end which are secured to the core wire; and a tapered extensionof the core wire extending distally beyond the distal end of the firstcoil; wherein the first coil is rotationally fixed with respect to thecore wire throughout the length of the coil.
 2. A flexible guidewire asin claim 1, wherein the first diameter is substantially equal to theouter diameter of the coil.
 3. A flexible guidewire as in claim 1,wherein the coil is snugly fitted around the flexible core wire.
 4. Aflexible guidewire as in claim 1, wherein the first diameter isapproximately 0.009 inches.
 5. A flexible guidewire as in claim 1,further comprising a second coil surrounding said tapered extension. 6.A flexible guidewire as in claim 1, wherein the core wire has a diameterof no more than about 0.009 inches.
 7. A flexible guidewire as in claim1, wherein the first coil comprises wire having a diameter within therange of from about 0.001 inches to about 0.003 inches.